there's an interesting thread on homes with two kitchens on Mumsnet - in UK it seams some people have overlooked that they may be classified as two residences with two lots of incredibly expensive council tax to pay if they have two kitchens ! it's worth a read if this is something you are considering, and you live in. the UK !
here's a link :
http://www.mumsnet.com/Talk/property/a1990876-Warning-about-buying-a-property-with-2-kitchens

Thank-you for that link, OnePlan! We are in the process of a 3-gen house hunt here in Scotland and a granny flat for my husband and I is rather high on the list - DH is out (again, on yet another consult, lol!) but when he comes in I'll ask him about that!

My son's US home (before the divorce) included a granny flat as when they built they had no idea I would remarry and relocate to the UK - we all thought after I retired I would retire to their granny flat. They used the granny flat for rental income except during the year after Hurricane Ivan when I lived in it. Now he (his son will be coming along too) is being job-relocated here to our area of Scotland we're going to be looking for a house to accommodate all three generations.

One of the things on the wish list is an en suite master on the main for DH and me but we did think a granny flat might be a good idea if we found a property with one. Granny flats are especially nice when there is an intact middle-generation, that way everyone has their own kitchen, lol!

When I stayed with my son and his then wife after the hurricane destroyed my home, having the granny flat was a huge benefit in that way especially (own kitchens). After I remarried five years later and had a five month wait for the paperwork to be sorted for a permanent return to the UK I stayed in their guest room as the granny flat had been rented on a long-term lease.

The single most important factor in that five month stay being successful was the three hours 'boundaries establishing' session we had the day after I arrived. I knew when it was my turn to cook, what amount of housecleaning and chores I could do without making my then DIL feel as though I was passively making a statement re her housekeeping, and how we were going to present a united face to the grandson, lol! He learned very quickly we were not going to be end-run:)

We bought a house about 5 yrs ago that was designed to house a mother-in-law who used a wheelchair at times...
There are two "master" suites--meaning both have en suite bathrooms...the 2nd bedroom has a wider than normal hall leading to it...
The room can accommodate a queen sz bed although we just have a twin/trundle in it with a computer armoire for my desktop.
The closet has swing-out double doors and a three sided shelf/rod arrangement that someone in a wheelchair could access easily and which makes a great storage closet for us...
The bathroom has roll-in shower stall but curiously not a raised-height toilet and (to me) the toilet doesn't seem to have easy acess if one were in a wheelchair...

The dishwasher is raised because it is on bar/island with sink that acts as space barrier between kitchen and downstairs LA...
using the dishwasher is maybe easier--
but again--the light switches are at normal height which seems counter intuitive for someone in wheelchair...thought they were supposed to be lower for easier access...

Another aspect of multi-generational living--
Our daughter moved to FL when she married and for long time they delayed having children. When we visited because they were living in small 1 bdroom condo, we stayed in local motels...
When they did decided to have a child, we started house shopping--especially since my husband was planning to retire within a year or two as well.
We were lucky enough to have the house next door to them come up for sale--and we bought it w/o even seeing it in person.
Being that close but with our own personal space has been wonderful. Our grandson is 20 mo old now and knows where "Nonna and Pappa" live (when we are in FL)...
The fact that we can go to our house and have our own space, live a separate life really, as we want/need to is what makes that closeness work.
Our daughter and SIL we think appreciate the help we can offer when needed (we were there recently for babysitting duty when our grandson's day care was foreclosed and our daughter couldn't find a place to take him). In fact, they are pretty sad to see us go when we return to our TX home.
In future, if they move to larger home in different area (and we are older ourselves), we might consider pooling our funds and looking for a situation where there is a smaller house on same property--like guest house--since I doubt we could find two individual next-door homes for sale at the same time.
It was just serendipity that this house came up for sale when we were looking...if we had bought one sooner, even in same neighborhood, and THEN their neighbors' house went up for sale we would have kicked ourselves every day for missing this chance.

We have built 2 multi-generational houses. Both houses have common areas and private areas, not a separate "granny suite". We share the living, dining, kitchen, mud/laundry, guest room, foyer and then we have separate bedroom/living areas. Myself, my husband and our 2 children share the house with my parents and we have lived in multi-generational houses for over 8 years. Our first house had my parents area on the main floor, and our bedrooms upstairs. Our current house is smaller with the living areas all on the same level. It has the common areas in the center and the private areas in wings on each side. We kept "accessibility" issues in mind when we designed the house; open-concept, level-entry, wheel chair accessible bathrooms. Both houses were general contracted by my husband and are ICF construction. Our current house has very a simple floor plan and roof line. Living in a multi-generational household requires communication, cooperation and mutual respect.

A thought with multi-generational living (if you're building a new home would be to design it using universal design concepts. I'll include 2 links below which may help you with this

www.udll.com

http://innovatebuildingsolutions.com/services/universal-design-accessible-remodeling

All I can say is that emotionally, it's the best way to go. Living independently and in isolation is overrated.

Kids calm down around grandparents, grandparents perk up around kids, parents get a helping hand, everyone is happy.